1. Field of the Invention
The present invention relates to an analog/digital characteristics testing device. In detail, the present invention relates to an analog/digital characteristics testing device for testing the analog/digital characteristics of an IC to be tested. Further, the present invention relates to an IC testing apparatus having a function of testing the analog/digital characteristics of an IC to be tested.
2. Description of Related Art
According to an earlier development, there is an IC testing apparatus (hereinafter, referred to as “IC tester”) comprising an analog/digital characteristics testing device for testing the analog/digital characteristics of an IC to be tested (hereinafter, referred to as “DUT”).
In this specification, the analog/digital characteristic(s) test means, for example, the test for the characteristic(s) of an analog-to-digital converter, the test for the characteristic(s) of a digital-to-analog converter or the like.
An analog/digital characteristics testing device according to an earlier development, is shown in FIG. 8.
As shown in FIG. 8, the analog/digital characteristics testing device 300 comprises a test controller 20, a plurality of analog/digital characteristics measurement circuits 21, 22, 23, 24, . . . , 2n. The n integrated circuits to be tested (DUT1 to DUTn) are connected with the analog/digital characteristics measurement circuits 21, 22, 23, 24, . . . , 2n, respectively.
The test controller 20 outputs a test condition data for the analog/digital characteristics test and a data write clock signal for writing the test condition data in the analog/digital characteristics measurement circuits 21 to 2n. Further, the test controller 20 manages a test result data outputted from each analog/digital characteristics measurement circuit 21 to 2n. 
Each analog/digital characteristics measurement circuit 21 to 2n comprises a computing circuit 21a, a memory 21b, a voltage measurement circuit 21c and a voltage generating circuit 21d. 
The test condition data outputted from the test controller 20 is stored in the memory 21b at a timing of the data write clock signal. Further, in the memory 21b, a measurement algorithm for measuring the analog/digital characteristics is previously stored.
In case that an object to be tested for the analog/digital characteristics is an analog-to-digital converter of the DUT, the computing circuit 21a controls the voltage generating circuit 21d to apply an analog signal to the analog-to-digital converter of the DUT by the voltage generating circuit 21d. 
The DUT outputs a digital signal corresponding to the applied analog signal. The computing circuit 21a stores the digital signal in the memory 21b. The computing circuit 21a controls the voltage generating circuit 21d to change the analog signal to be applied, and collects the necessary data for the analog/digital characteristics measurement.
When the necessary data is collected, the computing circuit 21a computes a data to judge whether the DUT is good or poor in accordance with the test condition data. The computing circuit 21a outputs the above judgment as a test result to the test controller 20.
In case that an object to be tested for the analog/digital characteristics is a digital-to-analog converter of the DUT, the computing circuit 21a applies a digital signal to the digital-to-analog converter of the DUT. The digital-to-analog converter outputs an analog signal corresponding to the applied digital signal. A voltage of the outputted analog signal is measured by the voltage measurement circuit 21c. 
The computing circuit 21a stores a measurement value obtained by the voltage measurement circuit 21c, in the memory 21b. The computing circuit 21a changes a digital signal to be applied, and collects the necessary data for the analog/digital characteristics measurement.
When the necessary data is collected, the computing circuit 21a computes a data to judge whether the DUT is good or poor in accordance with the test condition data. The computing circuit 21a outputs the above judgment as a test result to the test controller 20.
The analog/digital characteristics measurement circuits 22, 23, 24, . . . , 2n have the same structure and function as the analog/digital characteristics measurement circuit 21.
As explained above, the analog/digital characteristics testing device 300 according to an earlier development can comprise a plurality of analog/digital characteristics measurement circuits. However, because the analog/digital characteristics measurement circuit requires a voltage generating circuit and a voltage measurement circuit which are high precise and costly elements, the number of the analog/digital characteristics measurement circuits to be provided is the same as that of the DUTs which can be simultaneously measured by an IC tester, or is less than that of the DUTs, generally.
In case that a plurality of the analog/digital characteristics measurement circuits are provided in the analog/digital characteristics testing device, a plurality of DUTs are simultaneously measured by writing the same test condition data therein at the same timing with the data write clock signal. On the other hand, in case that a plurality of circuits to be tested for the analog/digital characteristics, which have different characteristics from each other, such as a plurality of analog-to-digital converters or digital-to-analog converters, are provided in one DUT, the analog/digital characteristics of these circuits cannot be simultaneously measured. That is, when a plurality of circuits to be tested for the analog/digital characteristics, which have different characteristics from each other, are provided in one DUT, it is necessary that a different test condition data should be written in each analog/digital characteristics measurement circuit in order to test the analog/digital characteristics of each circuit to be tested.
In general, because the DUT in which a plurality of circuits to be tested for the analog/digital characteristics, are provided, has a large scale, a number of pins for the logic function test are required. Therefore, the number of the DUTs which can be simultaneously measured by the IC tester, becomes small. When the analog/digital characteristics test for such a DUT is carried out, a plurality of analog/digital characteristics measurement circuits which are provided in the analog/digital characteristics testing device, are not effectively used.